Dual mode undercarriage for tracked vehicle

ABSTRACT

A vehicle with a frame connecting a driver wheel, an idler wheel and mid-roller wheels, an endless track belt being tensioned around the driver wheel and the idler wheel and being in contact with the mid-roller wheels on a lower run thereof, the mid-roller wheels being arranged in boogies, including a front boogie having a first pivot axis, a middle boogie and a rear boogie arranged in tandem having a second pivot axis, wherein the first pivot axis and said second pivot axis act as load transfer pivots.

FIELD OF THE INVENTION

The present invention relates to tracked vehicles. More specifically, the present invention is concerned with a dual mode undercarriage for tracked vehicles.

BACKGROUND OF THE INVENTION

A range of tracked vehicles, such as working vehicles, including asphalt pavers, crawlers, combine harvesters, earthmoving machines and transporters for example, experience shifts of their center of gravity or instabilities in balance, due to their carrying varying loads as they are used to spread material for example or to their supporting mobile heavy implements, or to high speed.

Indeed, it may happen that an additional weight due to material transported or unloaded or to an implement such as a screed on a paver for example, or a higher speed, destabilizes the vehicles, resulting in poor performance of the vehicles, premature failure of the traction system thereof, and damage to the underlying ground.

There is still a need for a dual mode undercarriage for tracked vehicles.

SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there is provided a vehicle with a frame connecting a driver wheel, an idler wheel and mid-roller wheels, an endless track belt being tensioned around said driver wheel and said idler wheel and being in contact with said mid-roller wheels on a lower run thereof, the mid-roller wheels being arranged in boogies, including a front boogie, a middle boogie and a rear boogie, the front boogie having a first pivot axis, and the middle and rear boogies forming a tandem having a second pivot axis, wherein the first pivot axis and the second pivot axis act as load transfer pivots.

Other objects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of specific embodiments thereof, given by way of example only with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a schematic view of a tracked vehicle according to an embodiment of an aspect of the present invention;

FIG. 2 is a view of a lateral belt arrangement of the vehicle of FIG. 1;

FIG. 3 illustrates the position of the axis of a rear tandem in the belt arrangement of FIG. 2, relative to the center of gravity of the vehicle;

FIG. 4 is a detailed view of the rear part of the lateral belt arrangement of FIG. 2;

FIG. 5 illustrates a behavior of the front part of the lateral belt arrangement of FIG. 2;

FIG. 6 show stoppers in an alternative of the belt arrangement of FIG. 2;

FIG. 7 illustrates a behavior of the rear part of the lateral belt arrangement of FIG. 2;

FIG. 8 illustrates the lateral belt arrangement of FIG. 2 in a first mode; and

FIG. 9 illustrates the lateral belt arrangement of FIG. 2 in a second mode.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is illustrated in further details by the following non-limiting examples.

As shown schematically in FIG. 1, a belt laying vehicle 100 comprises a track belt arrangement on each lateral side thereof, each track belt arrangement comprising an endless belt 12 entrained about an idler wheel 14 and a driver wheel 16 mounted in supporting relation to a frame 10, and mid-rollers 18. The frame 10 provides a flexible connection for the undercarriage including the wheels, the axles of the wheels, and the track belt 12. An implement 110, such as a screed for example, in the case of a paver, is located at one extremity of the vehicle, for example.

The vehicle is a tracked vehicle, such as a working vehicle, including for example asphalt pavers, crawlers, combine harvesters, earthmoving machines and transporters for example, which experiences shifts of its center of gravity or instabilities in balance, due to load distribution or speed for example.

As shown in details in FIG. 2, the endless track belt 12 is tensioned around the driver wheel 16, the idler wheel 14 and is in contact with the mid-roller wheels 18 on a lower run thereof. A tensioning system (not shown) allows controlling the tension of the belt 12, as well known in the art.

The mid-roller wheels 18 are here arranged as boogies including a front boogie 20 of axis 22, and rear boogies 24 and 26 assembled in a tandem 28 of pivot axis 30.

The center of gravity of the vehicle may be determined without load (see label CG_(empty) in FIG. 3), which corresponds to a maneuver mode, or travel mode, of the vehicle, and then with load thereon (see label CG_(loaded) in FIG. 3), which corresponds to a working mode of the vehicle.

In the case of an asphalt paver for example, CG_(empty) corresponds to the center of gravity of the paver when the hopper is empty and the screed is up; while CG_(loaded) corresponds to the center of gravity of the paver when the hopper is loaded and the screed is on the float.

The frame 10 is tiltable around the pivot axis 30 of the rear tandem 28, located between these centers of gravity of the unloaded and loaded vehicle, whereby a varying length of the belt 12 is pressed down into contact with the underlying ground 36. The positioning of the pivot axis 30 is a function of characteristics of the vehicle, such as for example characteristics of the screed in the case of a paver as discussed hereinabove, and may take into account security factors.

The adjustment further comprises providing stoppers 32 and 34 about the frame 10, as best seen in FIG. 4.

An up stopper 32 consists, for example, of a calibrated plate, welded to the frame 10, to which a part of the tandem 28 comes in abutment, thereby stopping the pivot movement of the tandem 28 around the axis 30. The position of the plate 32 is determined so as to allow a target range of forward tilt of the tandem 28 before abutment with the plate 32. In fact, the position of the plate 32 determines an angle at which the load on the vehicle is transferred on the undercarriage, and the extent of this transfer.

A down stopper may consist of a member 34, also welded to the frame 10 for example, which comes into abutment with a finger 39 of the tandem 28, thereby limiting the rearward tilt. This stopper 34 limits the tilt rearwards and protects the drive wheel 16 from impacts with the underlying ground.

The stoppers 32 and 34 are pre-adjusted, when assembling the vehicle, according to the characteristics of the belt, such as the hardness of the rubber for example, or the diameter of the drive wheel 16, to control the rotation of the axis 30 so as to use only a desired front or rear part of the belt 12. The part of the belt 12, which is not required for a current operation, is made to slightly lift off the ground 36 under action of the stoppers.

As the center of gravity of the vehicle passes over the pivot axis 30 of the tandem 28 to the front, the vehicle tilts towards the front, until the plate 32 stops movement of the tandem 28 about the pivot axis 30. At this point, the tandem 28 is fixed, and the vehicle may only pivot about the boogie 24. As the load increases, the center of gravity of the vehicle keeps shifting forwards and eventually reaches the level of the axis 22 of the front boogie 20.

As shown in FIG. 5, the axis 22 of the front boogie 20 supports and stabilizes the load in the working mode of the vehicle. The axis 22, located between the boogie 24 and the idler wheel 14, generally acts to limit the load on the idler wheel 14, by limiting the unbalance towards the front of the vehicle.

The axis 22 acts as a load transfer pivot until the center of gravity of the vehicle crosses the pivot axis 22 from the rear, as will now be described.

As the load increases and the boogie 20 sinks down into the track 12, the idler wheel 14 comes into contact with the underground surface, thereby limitating the sinking of the boogie 20 in the track by an upwards reaction (see arrow (A) in FIG. 5). Once the idler wheel 14 is in contact with the underground surface, any additional load is distributed between all mid rollers, with the axis 22 of the boogie 20 acting as a load transfer pivot (FIG. 5—arrows (B) and (C)).

Alternatively, in the case of a rigid belt 12′ such as a metal belt or a mixed metal and composite belt, as a substitute for the sinking of the boogie 20 into the resilient belt 12, it may be contemplated using a member, in rubber or in a deformable material, either added to the boogie 20 (see member 40 in FIGS. 6 a and 6 b), or included in the boogie 20 (see material 42 in FIG. 6 c), which deforms under load. In this case, sinking of the instead of the boogie 20 is obtained by deformation of this member.

As best seen in FIG. 7, in the working mode, the vehicle is tilted towards the front. As it does, the undercarriage structure, including the drive wheel 16, follows the movement, except for the tandem 28, which is stopped by the stopper 34. The drive wheel 16 is lifted up from the plane of the ground surface 36, thereby lying on a plane 33 different from the plane of the mid rollers 18 c, 18 d, 18 e and 18 f. The mid rollers 18 c and 18 d are in equilibrium under the load, and the mid roller 18 e becomes a stabilizator as the pressure from the belt 12 back on the mid roller 18 f acts as a tensioner, a cord being created between the drive wheel 16, which is lifted up, and the boogies 24 and 26, which remain on the ground.

Such actions and reactions interplay maintains the stability of the vehicle during accelerations, the rear tandem 28 allowing tensioning the track 12 during operations on the front part of the vehicle, i.e. on the rear end thereof as the drive wheel 16 is lifted from the ground 36, the rearest boogie 26 being in contact with the underground 36 with only one of the two mid-rollers thereof, the other one of the two mid-rollers thereof floating (see mid roller 18 f in FIG. 9) and acting for tensioning the track 12 in case of oscillation of the vehicle due to movement of the vehicle. The occasional load on the wheel 18 f on the ground 36, which tends to act on it upwards (see FIG. 7), acts on the floating wheel 18 f downwards, which tensions the belt 12 since the drive wheel 16 is off the ground, as described hereinabove.

Thus, the position of the tandem 28 is defined and adjusted to yield optimized load transfer performances, by controlling the position of supporting points and pivoting points depending of the load distribution on the vehicle, the vehicle operating from the maneuverability mode to the working mode as the center of gravity of the vehicle is shifted.

In FIG. 8, the center of gravity CG of the vehicle being located at the rear of the axis 30, the front idler wheel 14, the mid-rollers 18 a, 18 b and the rear drive wheel 16 are off the underlying ground 36, whereas the mid-rollers 18 c, 18 d, 18 e and 18 f are on the ground 36, maintained by stopper 34.

In FIG. 9, the center of gravity CG of the vehicle being located in front of the axis 30, the front idler wheel 14, as well as the rear drive wheel 16 and the rear mid-roller 18 f are off the ground 36, while the mid-rollers 18 a, 18 b, 18 c, 18 d and 18 e are on the ground 36, maintained by stopper 32.

Hence, according to the displacement of the center of gravity of the vehicle, different modes are allowed, which correspond to different conformation of the wheels and belt, as will now be described.

In the maneuverability mode, a short working surface of the endless belt 12 is achieved, as shown in FIG. 8, with only mid-rollers 18 c, 18 d, 18 e and 18 f on the ground 36.

In the working mode, the working surface of the endless belt 12 is increased, as shown in FIG. 9, with mid-rollers 18 a, 18 b, 18 c, 18 d and 18 e on the ground 36.

As people in the art will appreciate, the present system may be applied to utility tracked vehicles submitted to load shifts or unbalances, for a dynamic load and balance control.

For example, asphalt pavers, when they have a loaded hopper and screed on the float, i.e. before and during paving, typically benefit from the working mode described hereinabove, and, when the hopper is empty and the screed up once the paving operation is over, typically benefit from the mobility mode described hereinabove.

The present system and method provide increased stability, which results in increased traction quality and speed, and allows reducing mechanical wear and stress by optimized weight distribution and adaptable steering characteristics. People in the art will appreciate that the present invention therefore allows increasing the productivity of the vehicles and of activities making use of them.

The present undercarriage allows a dynamic control of load distribution, thereby optimizing performance and reliability of the vehicle, and constancy in traction characteristics while maintaining agility, stability and directional control of the vehicle.

Although the present invention has been described hereinabove by way of specific embodiments thereof, it can be modified, without departing from the nature and teachings of the subject invention as defined in the appended claims. 

1. A vehicle with a frame connecting a driver wheel, an idler wheel and mid-roller wheels, an endless track belt being tensioned around said driver wheel and said idler wheel and being in contact with said mid-roller wheels on a lower run thereof, said mid-roller wheels being arranged in boogies, including a front boogie, a middle boogie and a rear boogie, said front boogie having a first pivot axis, and said middle and rear boogies forming a tandem having a second pivot axis, wherein said first pivot axis and said second pivot axis act are load transfer pivots.
 2. The vehicle of claim 1, wherein said frame is tiltable around said second pivot axis, whereby a varying length of said belt is pressed down into contact with the underlying ground.
 3. The vehicle of claim 1, wherein said frame comprises a first stopper limiting a pivot movement of said tandem about said second pivot axis to the front, and a second stopper limiting a pivot movement of said tandem about said second pivot axis to the rear.
 4. The vehicle of claim 3, wherein said first stopper is a plate, a part of said tandem coming in abutment with said plate at a first angle of forward rotation of said tandem about said second pivot axis.
 5. The vehicle of claim 3, wherein said second stopper is a member, which comes into abutment with said tandem plate at a second angle of rearward rotation of said tandem about said second pivot axis.
 6. The vehicle of claim 3, wherein said first stopper stops a front movement of said tandem about said second pivot axis, as the center of gravity of the vehicle passes over said second pivot axis to the front.
 7. The vehicle of claim 3, wherein said first pivot axis transfers the load from the front to the rear until the center of gravity of the vehicle crosses said first pivot axis to the rear.
 8. The vehicle of claim 3, wherein, at an unbalance limit where said front boogie sinks relative to said belt, resulting in said idler wheel to come into contact with the underlying ground, said first pivot axis transfers the load from the front to the rear.
 9. The vehicle of claim 8, wherein said belt is in a resilient material, said front boogie sinking into said belt at said unbalance limit.
 10. The vehicle of claim 8, wherein said belt is one of: i) rigid and ii) semi-rigid, said front boogie comprising a member, said member deforming at said limit load; said front boogie sinking relative to said belt when said member deforms under said limit load.
 11. The vehicle of claim 1, wherein said first pivot axis acts as a transfer pivot to the rear until the center of gravity of the vehicle crosses said first pivot axis to the rear; and as the center of gravity of the vehicle passes over the second pivot axis from the rear, a first stopper prevents further tilt towards the rear, whereas as the center of gravity of the vehicle passes over the second pivot axis to the front, a second stopper prevents further tilt towards the front.
 12. The vehicle of claim 11, wherein said stoppers are pre-adjusted to control a rotation of the second pivot axis, to use only a desired part of the belt, a remaining part of the belt being made to slightly lift off the ground under action of the respective stopper.
 13. The vehicle of claim 11, said endless track belt being made in a resilient material, wherein said first pivot axis acts to limit a load on the idler wheel until a unbalance limit, said front boogie sinking into the belt and the idler wheel coming into contact with the underground surface at said unbalance limit; said first pivot axis, once the idler wheel is in contact with the underground surface, transferring any additional load to the rear of the vehicle.
 14. The vehicle of claim 11, said endless track belt being made in one a rigid or mixed material, wherein said front boogie comprises a deformable member, said first pivot axis acting to limit a load on the idler wheel until an unbalance limit, said deformable member being deformed and causing a sinking of said front boogie and the idler wheel to come into in contact with the underground surface at said unbalance limit; said first pivot axis then transferring any additional load to the rear of the vehicle.
 15. The vehicle of claim 11, wherein said endless track belt is made in a resilient material. 